1. Field of the Invention
This invention relates to hot tapping a piece of equipment which is in operation and contains a fluid material in the interior of that equipment. In particular, this invention relates to hot tapping such equipment by mechanical means with or without the use of a welding step.
2. Description of the Prior Art
Hot Tapping is a known, generic term and technique for creating an opening in piping, tanks, vessels, or other equipment (equipment) that is in operation, service, or use by drilling or otherwise cutting (drilling) an opening in that equipment. Often a branch fitting is attached during the hot tapping procedure. Hot tapping is desirably performed when it is not feasible or is impractical to take equipment out of service, or to purge or clean such equipment by conventional methods.
The American Petroleum Institute (API) has published written procedures directed to safe hot tapping practices in the downstream petroleum and oil processing industries. This API procedure is expressly limited to hot tapping by way of welding, and expressly excludes mechanical hot tapping because that form of hot tapping “is not common practice in oil processing and petroleum facilities”.
In contrast, the instant invention is directed to mechanical hot tapping in downstream oil processing and petroleum industry applications. Thus, this invention eliminates hot tapping by welding that is so common in those industries without eliminating the function thereof, and replaces it with a safer mechanical method.
Although this invention is applicable to a very wide variety of equipment in the downstream oil processing and petrochemical industries (industries), for sake of clarity and brevity this invention will be described hereinafter in respect of an atmospheric storage tank (tank).
A common method at present for installing, for example, a nozzle on the roof of a conventional carbon steel tank for pressure relief or other purpose, involves removing the tank from service, and cleaning and decontaminating it to a level that will allow welding of the nozzle on to the roof of the tank. Due to the nature of the hydrocarbonaceous fluid material held in the interior of the tank, the expense of isolating and decontaminating the tank is considerable. With a tank the size of a conventional storage tank out of use, extensive operational adjustments in the facility where the tank resides must be made in terms, for example, of temporary piping and tanks-in-service, in order to allow the subject tank to be taken out of operation. Due to the nature of the decontamination work aforesaid, there may be a potential for an environmental impact and safety consequences from this cleaning activity.
This invention eliminates (1) the need for removing the subject tank from use, (2) the environmental and safety risks that may be associated with the decontamination of the tank, and (3) the disruption of facility and process operations, and consequent modifications made necessary by the tank being removed from service. The cost savings realized by eliminating the foregoing can run into the hundreds of thousands of dollars.
When dealing with a hydrocarbonaceous fluid, flammability is a constant concern. With a flammable liquid and its associated vapor, there are three conditions referred to as the fire triangle that must be present in order for a fire or explosion to occur. First, there must be a volume of flammable hydrocarbonaceous fluid available. Tanks in the industries heretofore mentioned have more than sufficient quantities of such fluids present in order to afford a potential hazard. Second, the fluid must have oxygen available for mixing in correct quantities with the fluid vapor to form a mixture that is within the flammable envelope. Air is usually present in the industries aforesaid. Last, there must be an ignition source (heat) in the area of the flammable mixture.
This invention controls in a robust and fault intolerant manner two of the three legs of the fire triangle. Since the material normally stored in the tank is inherently flammable, there is little that can be done, short of the conventional methods described hereinabove, to reduce or eliminate the first leg of the triangle. This invention focuses on the other two legs, oxygen and heat, to prevent ignition. In this invention no single step is used to control oxygen and heat. Rather, multiple, redundant actions are taken pursuant to this invention to ensure that if a single protective step proves inadequate, sufficient safeguards remain to prevent undesired ignition.
It is also desirable to accomplish hot tapping of equipment without causing thermal degradation of the material stored or carried within that equipment.
Accordingly, it is desirable to have in the industries aforesaid a mechanical method for hot tapping equipment without taking that equipment out of service and with minimal risk of undesired vapor ignition or inventory decomposition.